Method and apparatus for simultaneously cold forming and stress relieving metal coils



A. H. BITZER, JR

June 6. 1967 METHOD AND APPARATUS FOR SIMULTANEOUSLY COLD FORMING AND STRESS RELIEVING METAL COILS Filed Feb. 17, 1964 United States Patent .Ofi Yice 3,323,346 Patented June 6, 1967 3,323,340 METHOD AND APPARATUS FOR SINIULTANE- ULY COLD FORMING AND STRESS RELIEV- ING METAL COlLS Albert H. Bitzer, Jr., Kenilworth, Ill. Illinois Coil Spring Company, 2100 N. Major Ave., Chicago, Ill. 60639) Filed Feb. 17, 1964, Ser. No. 345,220 2 Claims. (Cl. 72-135) This invention pertains generally to the art of stress relieving metal parts, and refers more particularly to a method and means for normalizing coiled springs.

It is well known that a newly formed or green spring coiled by heretofore conventional methods has certain internal stresses which result from the coiling operation and which are, for the most part, unpredictable. The presence of these internal stresses is undesirable because the stresses produced by any external load upon the spring are vectorially added to the internal stresses already present in the spring, and hence even a relatively small load might permanently deform a spring having high residual stresses because of the total of load and residual stresses exceeding the elastic limit of the spring material.

The process of relieving internal stresses in a spring is known as normalizing, and has always heretofore been accomplished by heating the green spring to some predetermined temperature, usually around 500 F. Such heating did not significantly affect the grain or crystalline structure of the metal comprising the spring but apparently permitted a molecular reorientation of the spring material whereby the stresses in it were relieved to a greater or lesser extent. The duration and temperature of the normalizing heat varied with such factors as the size and nature of the spring material and the application for which the spring was intended, and were determined on the basis of experiment and experience.

Normalizing has sometimes been effected by electrical resistance heating, but has usually been carried out in an oven into which baskets filled with green springs were loaded. Hence the requirement for a normalizing oven or ovens complicated the process of manufacturing coiled springs and very definitely increased the cost thereof. Besides being costly to operate, a normalizing oven is a relatively bulky and expensive piece of equipment, and its presence in a manufacturing plant entailed a need for various safety devices and precautions, to say nothing of the uncomfortable conditions that an oven tended to create during Warm weather.

The present invention has for its principal object the 7 complete elimination of the normalizing process as such in the manufacture of coil springs, and the production of springs which are normalized during the coiling operation. Moreover it is an object of the present invention to achieve normalizing of coiled springs without heat treating them, thus greatly increasing both the safety and the comfort of personnel engaged in the manufacture of such springs.

The invention rests upon the discovery that'the internal stresses in metal parts can be relieved by subjecting such parts for a relatively brief interval to ultrasonic vibration at frequencies on the order of 20 to 100 kilocycles and of relatively low amplitude. It has been found that the required duration of the ultrasonic treatment is so brief that it can be effected concurrently with the coiling of a spring, and that the amplitude of the vibration is so low that power requirements for the ultrasonic treatment are much lower than those for heat normalizing.

Thus it is another object of this invention to provide a method and means for normalizing coiled springs as the same are being coiled, without the application of either heat or electric current to the springs, and at lower cost than was entailed in prior normalizing processes involving heating of springs.

Another object of this invention is to provide means for applying the above mentioned discovery to the formation of coiled springs on a conventional spring coiling machine without requiring substantial modification of the machine and without slowing down its production capacity.

With the above and other objects in view, this invention resides in the novel method and means devised for the practice thereof, as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise method and means herein disclosed may be made as come within the scope of the claims.

For a more complete description of this invention, reference is now made to the accompanying drawing which illustrates one embodiment of the invention according to the best mode so far devised for carrying out the same, and in which:

FIGURE 1 is a fragmentary elevational view of a spring coiling machine which is generally conventional except that it has means for imparting ultrasonic vibration to its coiling point in accordance with the principles of this invention; and

FIGURE 2 is a more or less diagrammatic detail elevational view on an enlarged scale showing the relationship of arbor, coiling point, and wire stock being coiled, in a coil winding machine embodying the principles of this invention.

Referring now more particularly to the accompanying drawing, the numeral 5 designates generally the frame of a spring coiling machine of a known type, examples of such machines being disclosed in Patent No. 3,068,927, to C.R. Bergevin, and the patents therein referred to. In such machines, a continuous length of wire stock 6 is drawn from a source thereof (usually a reel, not shown) by feed rolls 7 and 8 which cooper-ate with grooved wire guides 9 and 10 to drive the wire lengthwise forwardly toward a coiling point or coiling abutment 11.

As is conventional in such spring coiling machines, the wire passes either over or under a fixed arbor 12 as it moves forwardly toward the coiling point, and the coiling point, depending upon the position to which it is adjusted, deflect-s the wire either downwardly or upwardly, bending the wire as it is fed forwardly and causing it to coil around the arbor. The coiling point is spaced forwardly of the arbor, and the diameter of the coils of the finished spring is established by adjustment of the coiling point toward and from the arbor. Thus the feed rolls, arbor and coiling point constitute cooperating forming elements by which the wire is formed during .the coiling operation, and the forming of the wire takes place in consequence of movement of the feed rolls, 'by which the wire stock is constrained to lengthwise move-ment while the other two forming elements remain relatively stationary.

When a predetermined length of wire has been fed forwardly, depending upon the number and size of the coils desired in the finished spring, a cut-off element 13 operates to sever the coiled length of wire from the rest of .the wire stock, thus completing the formation of the green pring in the heretofore conventional practice of the spring coi ing process.

With a coil Winding machine that has been modified in accordance with the principles of the present invention, a heat treating or normalizing step subsequent to the coiling operation is not needed because normalizing is effected substantially concurrently with the coiling of the spring, by reason of the fact that the coiling point 11 is continuously vibrated at an ultrasonic frequency during the coiling operation. Thus it is a feature of the present invention that the spring material is stress relieved during and directly subsequent to the bending ope-ration by which it is formed into a coil, by the step of subjecting it to ultrasonic vibration as it moves through the bending zone.

The specific means for imparting such ultrasonic vibration to the coiling point comprises an ultrasonic transducer 15 upon which the coiling point is mounted, and an oscillator-amplifier 16 which is electrically connected in energizing relation with the transducer. The transducer 15 can be of a know type, having a horn or vibratory element 17 which is axially elongated in the direction of its vibratory motion and which terminates in -a tip 18 of relatively small area. Such a transducer is disclosed, for example, in Patent No. 3,066,232 to N. G. Branson for Ultrasonic Transducer. The coiling point 11, which can be for-med of carbide, can be mounted on the tip 18 of the transducer horn in any suitable manner that assures transmission to the coiling point of the vibrations of the transducer tip. Very satisfactory results have been obtained by brazing a solid carbide coiling point to a holder 19 of SAE 1010 steel which is threaded into the tip of the transducer horn.

The transducer, in turn, is mounted upon a slide 20 which is horizontally movable in the frame of the machine, and which is a generally conventional element in a spring coiling machine. Normally the slide would carry a swingable arm, upon the free end of which the coiling point would be mounted, but in this instance the arm is replaced by the transducer, which is held in place by means of a collar 21. Some reworking of the slide may be necessary to accommodate the collar 21, but this constitutes the only modification of an otherwise conventional coiling machine that is needed for practicing the present invention in the coiling of springs.

The oscillator-amplifier 16 is of a known type. It can be mounted at any convenient location and connected with the transducer by means of a flexible conductor cable 23 which does not interfere with movement of the transducer on and with the slide 20. The frequency of the output current of the oscillator-amplifier should of course correspond to the frequency for which the transducer is designed. Very satisfactory results have been obtained with frequencies on the order of 20 kilocycles per second. Apparently the frequency is not critical, at least within the ultrasonic range to about 100 kilocycles per second.

A vibration amplitude of about .003 inch has been found adequate for the purposes of spring manufacture, requiring a power on the order of 75 watts to 150 watts for processing small springs. From these figures it will be obvious that the present invention affords substantial savings in power required for normalizing as compared with prior heat treatment processes.

With the method and apparatus of this invention there is no need for slowing the spring coiling machine below its normal operating speed. Stress relieving takes place in the very short time that the wire stock is passing through the bending zone in spring coiling operation.

It is not known why internal stresses in a metal part are relieved when the metal is subjected to ultrasonic vibration, but it is possible that the energy imparted to the molecules of the metal by such vibration tends to relax their cohesion and permit the-m to achieve the desired reorientation. If this theory is correct, it would seem that the mechanical energy of ultrasonic vibration is more efficient for effecting such molecular reorientation than the heat energy heretofore commonly used for normalizing.

Whatever the reason, it has been found that springs wound in accordance with the principles of this invention not only possess the same desirable characteristics as springs normalized by heat treatment, but in addition exhibited substantially less variation in free length, increased load capacity, and decreased variation in ratio of load to deflection from spring to spring. This increased uniformity stems, no doubt, from the fact that each pring receives exactly the same treatment, whereas in normalizing by baking, uniform treatment of all springs is a practical impossibility. To be at all commercially feasible, the baking of springs must be done in batches which results in some springs receiving more heat than others.

It has also been observed that springs coiled in accordance with the present invention display substantially less surface scuffing and abrasion than those coiled against a non-vibratory coiling point. While such scuffing as existed on prior springs, due to friction between the spring stock and the coiling point, was insignificant for the great majority of applications, there may be casesas where appearance is importantwhere the decreased scuffing attributable to the method of this invention might be sufficient in itself to warrant its use in the coiling of springs. The reason for the decreased scufiing is not known, but it is possible that because of the vibratory motion of the coiling point the spring stock is out of actual contact with the coiling point during a substantial portion of the time that it is traversing it, thus minimizing friction between the stock and the coiling point. Another factor contributing to the reduced scuffing may be the fact that normalizing is taking place concurrently with bending, so that less energy is required to form the stock into a coil, the effect being somewhat similar to coiling the stock while holding it at a substantially elevated temperature but without, however, affecting the grain or crystalline structure of the metal.

Another advantage which the present invention has over the conventional normalizing-by-heat process, is that it permits using pre-plated wire where plating is required for the sake of appearance since such contact that takes place between the vibrating coiling point and the wire as it is being coiled leaves the surface of the wire unmarred; whereas with the prior practice there was not only some noticeable scuffing of the surface of the coils, but very often the plating could not withstand this normalizing heat treatment. Hence, with the prior practice it was necessary to plate the springs after they were fully formed and normalized.

From the foregoing description taken together with the accompanying drawings it will be apparent that this invention provides a novel method and means for stress relieving metal parts, which is especially significant and useful in the production of coiled springs, since it eliminates the need for a heat treating operation to normalize the springs, and thus :greatly reduces the cost of making springs, while at the same time assuring more uniformity in the springs produced.

What is claimed as my invention is:

1. In the method of coiling a metal spring by forcing wire stock lengthwise against a coiling point and around an arbor, the characteristic step of: imparting ultrasonic vibrations to the wire at the coiling point by vibrating the coiling point at ultrasonic frequency as the wire is being forced against it.

2. In spring coiling apparatus of the type having an arbor, means for forcing wire stock lengthwise past the arbor, and bending means including a coiling point having ultrasonic vibratory reciprocation cooperating with the arbor to bend the wire in a bending zone adjacent to the coiling point and thus coil the wire, and means for imparting said ultrasonic vibratory reciprocation to said bending means in the bending zone, said means compris- (A) means for generating an alternating current of ultrasonic frequency;

5 6 (B) an ultrasonic transducer; References Cited (C) conductor means connecting said alternating cur- UNITED STATES PATENTS gf i f s f means Sald ultrasmlc trans 2,841,201 7/1958 Cheatle 7z 141 5 2,995,050 8/1961 Karron et a1. 72205 (D) vibration transmitting means connecting the coiling point with the transducer so that the coiling CHARLES LANHAM: Prlmary Examine"- point vibrates at ultrasonic frequency. R. D. GREFE, ssi Ex mine 

1. IN THE METHOD OF COILING A METAL SPRING BY FORCING WIRE STOCK LENGTHWISE AGAINST A COILING POINT AND AROUND AN ARBOR, THE CHARACTERISTIC STEP OF: IMPARTING ULTRASONIC VIBRATIONS TO THE WIRE AT THE COILING POINT BY VIBRATING THE COILING POINT AT ULTRASONIC FREQUENCY AS THE WIRE IS BEING FORCED AGAINST IT. 